Those skilled in the art appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. In conventional overhead valve internal combustion engines, a pair of valves reciprocates in timed alternation to provide intermittent communication between the intake and exhaust manifolds and a combustion chamber.
The intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve, which permits fuel mixed with air to flow into the combustion chamber. In addition, at least one exhaust valve and associated exhaust port are utilized for releasing expended combustion gases from the chamber.
In order to reduce wear associated with moving valve parts, lubrication is provided to the upper portions of the valves. However, because temperatures in the combustion chamber may approach or exceed 1000 degrees Centigrade, any lubricating oil exposed to these temperatures will vaporize or burn leaving behind deposits that may interfere with the proper sealing of the valves and cause rapid deterioration. Valve stem seal assemblies are used to seal against leakage of oil between each valve guide and its associated valve stem.
It is, therefore, necessary to at least provide seals around the upper region of the valve stems and along the valve guide. A typical valve stem seal has a generally cylindrical shape that is partially closed at one end. The cylindrical region seats about the valve guide to maintain the valve seal in a stationary position. The upper region of the valve stem is surrounded by the valve seal when the valve stem is fully inserted into the valve seal assembly.
However, all valve seals have limits as to how much guide-to-stem eccentricity (radial misalignment) they can handle and still adequately seal the valve stem. This can present itself statically from machining issues where the guide ID and OD are not machined concentrically to each other. This can also present itself dynamically when, during engine operation, the valve stem deflects (from stem-to-guide clearance or bending) which will increase loading on one side of the sealing lip and decrease loading on the opposite side of the sealing lip, possibly to the point of losing contact.
A traditional Dana Allbond™ seal assembly 5 (see prior art FIG. 1, owned by the common assignee, Dana Automotive System Group, LLC, Maumee, Ohio) was developed to solve the problems that valve seals encounter in engines that operate with manifold pressures in excess of 350 kPa. While the full metal reinforcement afforded by the extended metal retainer 6 of the traditional Allbond™ seal assembly 5 assists with resisting manifold pressure it, however, creates a seal assembly 5 that is not very radially compliant.
It appears that these problems with such valve stem seal assemblies 5 are a result of the upper and lower portions 7, 8 becoming mechanically coupled together, such that both upper and lower portions 7, 8 bend with a rigid stem (see, stem 62 in FIG. 3). In order to become eccentricity tolerant, somehow the upper portion 7 and the lower portion 8 of the seal assembly 5 need to move more independently of each other, possibly by making the seal assembly 5 more radially flexible. At the same time, however, the upper sealing lip 9 cannot be pulled too far toward the stem beyond its free state or else the upper lip 9 will leak oil and port gasses.
A further design constraint that needs to be considered is that, under high manifold pressures, the upper portion 7 of the seal assembly 5 has a force F (see FIG. 3) applied to it that wants to push the upper portion 7 of the seal assembly 5 upward and away from the lower portion 8 of the seal assembly 5. This in turn stretches the rubber (synthetic or actual) section between the metal stampings and creates stress risers in the rubber which could lead to tears in the upper portion 7. A means, therefore, is also sought to limit the axial displacement of the upper portion 7 of the seal assembly 5 when analysis shows that this is necessary.
U.S. Pat. No. 6,722,657 is an example of related art, which discloses a radial seal 100 for sealing an annular gap (not identified) defined between a bore 24 of a housing 90 and an outer surface of a cylindrical shaft (see axle 80). The seal comprises inner and outer rings 30 with foam seal elements 64a, 64b therein. Thereby, the seal forms a labyrinth (see area taken up by foam elements) that is subsequently filled with a highly viscous fluid 85.
Further, U.S. Pat. No. 6,655,693 shows a non-contacting gas compressor seal assembly that is positioned between a housing of, for example, a gas compressor and its rotatable shaft. The seal assembly contains the gas from passing between the shaft and the housing to the surrounding environment.
In addition, U.S. Pat. No. 5,558,056 discloses a valve stem seal that utilizes a finger spring 26, which is molded in a resilient body 24 that is used to keep an annular lip 28 in the resilient body in radial contact with a valve stem 12.
In U.S. Pat. No. 5,183,351, a boot retainer mechanism 133 retains a boot 112 on a joint 110 by way of bands 124, 132. The bands are coaxial with the central axis 140. Two flanges 144, 146, which are radially placed, cooperate with the bands to seal a shaft 116.
Also, U.S. Pat. No. 5,174,256 discloses a valve stem seal 10 that utilizes a spring 24 that applies a compressive force on a lip to seal a resilient seal to a valve stem 18. Two shells 12, 14 are allowed to move with respect to each other in order to allow for adjusting the guide height of the valve seal.
Lastly, U.S. Pat. No. 4,909,202 teaches a valve stem seal 10 encased in a shell 12. The seal body 14 is one piece where the shell acts to give support to a lip (not identified) that provides the sealing of the body to a valve stem 40.
Even with these means of sealing a reciprocating valve stem, none of the seals provide a means of sealing that is tolerant of the eccentric motion of a valve stem and particularly for engines exposed to high manifold pressures. As a result, a seal that is eccentrically tolerant to valve stem motion is sought.